The invention relates to a drive train of a motor vehicle comprising an internal combustion engine having at least one electrical motor which can be operated as a generator connected to the engine, a stepped automated manual transmission and at least one control device for controlling the internal combustion engine, the at least one electrical motor and the stepped automated manual transmission, and also to a method for controlling the operation of such a drive train.
In vehicles comprising an internal combustion engine and an electric motor as drives, the electrical motor is advantageously also operable as a generator in order to recover braking energy (recuperation).
DE 195 28 628 discloses a hybrid drive for a motor vehicle comprising an internal combustion engine and an electric motor as drives, in which hybrid drive the electric motor can be operated as a drive motor, generator or as a synchronizer for a change-speed transmission. The generator power of the electric motor is controlled in such a way that an approximately equal vehicle deceleration is achieved in all gears. If a gear change is to be initiated, the internal combustion engine is first disconnected from the drive shaft of the transmission by a clutch and, at the same time, the electric motor is activated as a synchronizer. The purpose of operation of the electric motor during the gear-shifting operation is therefore no longer recuperation but acceleration or braking of the drive shaft to the rotational speed which is required for the transmission ratio to be selected. When shifting to a lower gear, in the case of which the rotational speed of the internal combustion engine has to be increased for the engagement of a lower gear, the electric motor accelerates the drive shaft. Therefore, no braking energy can be recuperated during the gear-shifting operation to a lower gear.
In vehicles with a conventional internal combustion engine drive and a stepped automated manual transmission, it is known that, for reasons of comfort, shifting times when shifting down to a lower gear are extended by approximately 0.5 second to 1 second when the vehicle is coasting. This is known as coasting shifting.
The noticeable jerk when selecting the lower gear or the acceleration of the internal combustion engine which is required as a result can be avoided, for example, by a continuously variable transmission (CVT) being used instead of a stepped manual transmission.
US 2003/0168266 discloses a control means for a braking system which comprises an electrical machine which can be operated as a generator, a CVT transmission and a control device. The recuperation torque of the electrical machine is transmitted to a drive wheel via the gears. In order to avoid an excessively high braking torque on the drive wheel, the recuperation torque of the electrical machine is limited as a function of the transmission ratio i. Therefore, if the transmission ratio i increases, the maximum possible recuperation torque becomes smaller.
It is the object of the present invention to maximize the recuperation energy in a vehicle without any losses in comfort and also to increase vehicle safety.